Heat sensitive switch



' Aug. 13, 1940.

M. .J MAYNARD 2,211,700

HEAT SENSITIVE SWITCH Filed May 14, 1938 INVENTOR Meade Jo Mmgnuwdb ATTORNEY Patented Aug. 13,1940

UNITED STATES PATENT OFFICE HEAT SENSITIVE SWITCH ware Application May 14, 1938 Serial No. 208,022

13 Claims.

This invention relates to the art of thermostatic switches, and more particularly to that type v as soon as the flame is extinguished. In order to produce such a function it is obvious that the switch must operate independently of any definite temperature value and respond only to a reversal of temperature change over that which caused the last switch actuation. It is a further requisite that the switch be very sensitive to any movement of the temperature responsive device.

It is a prime object of this invention to provide a switch which will fulfill the above requirements.

A further object is to provide a heat responsive device which buckles a member by applying an endwise pressure upon it.

A further object is to provide a device of the type set forth in the preceding paragraph wherein the buckling member is a leaf spring and carries a switch contact at an intermediate point.

A still further object is to provide a frictional mounting for one end of said spring so that the switch will be actuated upon a change in the direction of movement of the heat responsive device.

A still further object is to provide a means for adjusting the amount of friction afforded by said frictional mounting and adjustable stops for limiting the buckling movement of the leaf spring.

Another object of this invention is to provide a switch of the above type in which a relative movement will occur between the contacts after they are made, which will aid in keeping them clean.

Although this switch is particularly adapted for use in connection with an oil burner control, it will readily be understood that it may also be used in various other types of systems.

These and other objects will readily become apparent as the following specification is read in the light of the accompanying drawing, in which Figure 1 is a cross-section of a device em-- 5 0- bod'ying my invention, and

' Figure 2 is a view of one of the details of construction.

The present switch mechanism is' adapted to be actuated by means of a metallic diaphragm H which closes the end of a cup-shaped member l2. A washer 3 of a soft metal lies adjacent the diaphragm II and the three members are secured together by means of screws, one of which is shown at l4. An elongated tube I5 is provided with a flange l6 which has a series of 5 holes, one of which is shown at IT, through which bolts |8 are inserted to clamp an annular piece of heat insulating material l9 between the flange I6 and the washer l3 by means of nuts Ill. The cup-shaped member I2 is provided with a hole 10 20 through which is inserted a connecting rod 2| which has a reduced end portion 22 which is screw-threaded and inserted through a small hole 23 in the center of the diaphragm The connecting rod 2| is secured to the diaphragm by means of a nut 24 threaded on the screw-threads 22. The connecting rod 2| is provided at its opposite end with an enlarged head 25. A compression spring 26 surrounds a portion of the connecting rod 2| and is confined by two spring 20 retainers 21 and 28, 21 lying adjacent the cupshaped member l2 and 28 lying against the head 25.

The head 25 is connected to one end 29 of a fiat leaf spring 30 by means of a pin 3|. A 25 on the upper face of the end 36 of the leaf spring 35 i is a washer 38 and a screw 39 is inserted downwardly through the -washerand the slot 31 and is screw-threaded in the hole 35 in the sleeve 34. The screw 39 confines between its head and the washer 38 a compression spring 48. Adjustment 40 of the screw 39 in the hole 35 will vary the force exerted by the spring 40 on the washer 38, thereby varying the force with which the washer 38 bears against the end 36 of the spring 30. The purpose of this arrangement is to provide an ad- 45 justment of the resistance to movement of the end 38 of the spring 30 by the washer 38 and sleeve 34.

The bracket 32 is provided with a hole 4| about which is attached a piece of insulating material 5 42 by means of screws 43. A stationary contact 44 is mounted on a screw 45 which is adjustably threaded to the insulating material 42 and whose stem is smaller in diameter than the hole 4| so that the contact will be electrically insulated 55 standing arm e1 having a horizontally extending portion 48 through which is adjustably threaded a stop member 49. It will be noted that the stop 49 is so adjusted that the leaf spring 30 can never assume a straight position so that'when the diaphragm H moves toward the left the spring is bound to buckle so that the movable contact 66 will be moved in a downward direction. It will be noted also that the compression spring 26 so biases the diaphragm l I that as it expands it will always move toward the left.

The tube I is adapted to be positioned in the wall of a furnace, for example, so that the diaphragm II will look directly toward a source of radiant heat such as the flame produced by an oil burner. In order that the diaphragm shall be more sensitive to such heat radiations the surface which looks toward the source is blackened.

In Figure 1 the parts are shown in their cold position. Assume now that the source of radiant heat towards which the diaphragm ll faces increases in temperature so that the diaphragm will absorb an additional amount of heat. This will cause the diaphragm to expand but as the periphery of the diaphragm is prevented from moving the center must buckle and due to the bias of the spring 26 this buckling will move the connecting rod 2! toward the left. The spring retainer 28 moves with the rod 2| and is guided by the bracket 32' and a bracket 50 which is connected to cup l2 by means of screws 5|. The spring M has been so adjusted as to resist the movement of the end 36 of the spring 30 toward the left so that as the connecting rod 2i moves toward the left the spring 30 will buckle near its center and cause the movable contact 46 to enage the stationary contact M. This will prevent spring 30 from buckling further and any furthermovement of the connecting rod to the left will be accommodated by the end 36 of the spring 30 slipping between the sleeve 35 and washer 3,8a's permitted by means of the elongated slot 37. As long as the diaphragm I I does not decrease in temperature, the contacts 46 and 46 will remain in engagement, but as soon as the source of radiant heat decreases in temperature the diaphragm II willimmediately start to move towards the right, causing the connecting rod 2|. to pull-the end 29 of ,the spring 30 towards the right. The immediate efiect of this movement will be to straightenthe spring 30, which will cause an upward movement of the movablecontact 46, which movement will continue until the stop 49 is engaged. Further movement. of the connecting rod 2| toward the right caused by continued cooling of the diaphragm II, will now cause theend 36 ofthe spring 30 to move toward the right by slipping between the sleeve 34 and the washer 38 by means of the elongated slot .31. This returns the parts to the position shown inFigure 1 where they will be ready to repeat the above cycle indefinitely.

From the above it willbe seen that the present switch .will function to control the circuit not in, response to the attainment of any particular temperature value but rather immediately upon the occurrence of a change in temperature in a direction opposite to that which caused the last switch operation. It will also be seen that a decided mechanical advantage is obtained, causing the movable contact 66 to move a relatively large distance in response IO a relatively small movement of the diaphragm II. This mechanical advantage is of course due to the buckling of the spring 30.

This switch could very easily be made into one which would open the contacts on temperature rise by merely reversing the position of the stop 49 and the stationary contact 45. The screw 39 is very easily and readily capable of adjustment for varying the amount of friction imposed by spring 40 upon the movement of the end 86 of the spring 30 so that it may be adjusted with respect to the type of spring used.

Certain other changes and modifications of this invention may readily occur to those skilled in this art and it is therefore to be understood that I intend to be limited not by the specific embodiment disclosed but rather by the scope of the appended claims.

I claim as my invention:

1. In a device of the character described, an operating member, means for supporting one end of said member and frictionally resisting movement thereof, and a condition responsive device for applying a longitudinal pressure to the opposite end of said member to cause it to first bend laterally and then move longitudinally.

' 2. In a device of the character described, an operating member, means for supporting one end of said member and frictionally resisting movement thereof, a condition responsive device for applying a longitudinal pressure to the opposite end of said member to cause it to first bend laterally at an intermediate portion and then move longitudinally, and stops for limiting the amount of said lateral movement, one of said stops preventing said member from assuming a straight position after said longitudinal pressure is removed. 4

3. In a device of the character'descri-bed, an operating member, means for supporting one end of said member and resisting movement thereof, a condition responsive device for applying a longitudinal pressure to the opposite end of said member to cause it to buckle thereby causing a lateral movement of an intermediate portion, stops for limiting the amount of said lateral movement, one of said stops preventing said member from assuming a straight position after said longitudinal pressure is removed, said means permitting longitudinal movement of said memher after it has engaged one of its stops, and

control means operated by said intermediat portion. a

4. In a device of the character described, :an elongated leaf spring, frictional mounting means for one end of said spring, stops on opposite sides of an intermediateportion of said spring, a heat responsive device for applying a longitudinal pressure to the other end of said spring on a variation of the heat in one direction to cause said spring to buckle and move said intermediate portion from engagement with one stop into engagement with the other, further movement or said heat responsive device being permitted by said one end of said spring slipping in said frictional mounting, and means for first moving said intermediate portion into engagement with said one stop and then causing slippage of said one end of said spring in said frictional mounting means upon a reversal in movement of said heat responsive device.

5. In a device of the character described, an elongated leaf spring, frictional mounting means for one end of said spring, stops on opposite sides 1 an intermediate portion of said spring, a heat responsive device for applying a longitudinal pressure to the other end of said spring on a variation of the heat in one direction .to cause said spring to buckle and move said intermediate portion from engagement with one stop into engagement with the other, further movement of said heat responsive device being permitted by said one end of said spring slipping in said frictional mounting, means for first moving said intermediate portion into engagement with said one stop and then causing slippage of said one end of said spring in said frictional mounting means upon a reversal in movement of said heat responsive device, and an electrical contact carried by said intermediate portion of said spring, one of said stops being adjustable and providing a stationary electrical contact.

6. In a device of the character described, an elongated leaf spring, frictional mounting means for one end of said spring, stops on opposite sides of an intermediate portion of said spring, a heat responsive device for applying a longitudinal pressure to the other end of said spring on a variation of the heat in one direction to cause said spring to buckle and move said intermediate portion from engagement with one stop into engagement with the other, further movement of said heat responsive device being permitted by said one end of said spring slipping in said frictional mounting, means for first moving said intermediate portion into engagement with said one stop and then causing slippage of said one end of said spring in said frictional mounting means upon a reversal in movement of said heat responsive device, and means for varying the amount of friction produced by said frictional mounting.

7. A control device of the character described,

' comprising in combination, a leaf spring, means for supporting one end of said spring, means resisting longitudinal movement of said one end of said spring, condition responsive means for alternately moving the other end of said spring toward and away from said one end, causing said spring to alternately bow in the middle and straighten out, and a stop for limiting the amount' said spring can bow, said resisting means permitting said one end to move longitudinally in one direction after said stop has limited the bowins of said spring, and in the other direction after said spring has been straightened out.

8. In combination, a condition responsive device, a leaf spring having one end attached thereto, a support for the otherend, spring means normally resisting but being capable of permitting longitudinal movement of said other end, and stops to limit the movement of the center portion of said spring, whereby said leaf spring first moves laterally to engage one of said stops and then moves longitudinally.

9. In a device of the character described, an

elongated leaf spring, a condition responsive de-.

vice connected to one end of said spring for causing longitudinal movement thereof, a support for the other end of said leaf spring, means for'normally resisting but being capable of permitting longitudinal movement of said other end of said leaf spring including an adjustable spring, adjustablestop means cooperating with an intermediate portion of said leaf spring for keeping it at least partially bowed, a movable contact carried by said intermediate portion, and a stationary contact for cooperation with said movable contact, said stationary contact also limiting the amount which said leaf spring can bow under the influence of said condition responsive device.

10. In a device of the character described, a metallic diaphragm for receiving radiant heat from a source, means for fixing the periphery of said diaphragm, an elongated operating member,

means connecting the center of said diaphragm .tially immediately upon reversal of movement of said diaphragm, said means comprising an elongated leaf spring connected at one end to said diaphragm and frictionally mounted at its other end.

12. In a device of the character described comprising in combination, a circuit controlling member, a device for exerting a longitudinal force on said member in response to variations in the value of a variable condition, and friction means for first causing said member to move laterally and perform its circuit controlling function in response to a change in said condition value and thereafter permit longitudinal movement of said member upon further variations of said condition value.

13. In a device of the'class described, a flexible circuit controlling member both ends of which are confined against lateral movement, a condition responsive device for placing a longitudinal force on said member to cause it to bend in the middle in response to variations in the value of said condition, means limiting the amount which said member can bend and slip friction means permitting further movement of said condition responsive device after the lateral movement of said member has been stopped.

MEADE J. MAYNARD. 

